The subject matter of the present invention is a hook system for a sewing machine.
Hook systems are known. The hook system of the sewing machine guides the upper thread around the lower thread so that a knot can be formed.
The present hook system is a hook system that makes possible a CB-hook-type knot formation. In such hook systems, the upper thread loop, which is guided around the lower thread, is not rotated or twisted; rather, the upper thread runs around the lower thread in a U shape and consequently pulls the lower thread untwisted into the sewed material at the underside. In order to be able to do this, the loop of the upper thread must be guided around the hook body, with the bobbin and the bobbin case situated therein, by the hook tip. This means that the hook body, or hook for short, is not connected to the hook driver via a shaft, but rather is freely mounted in a hook race, and can be set into rotation by the hook driver using suitable means. The further problem occurs here that the upper thread and also the lower thread are braked in irregular fashion by the elements of the hook system, so that changes in thread tension caused by this are detectable later in the stitch pattern.
In such hooks mounted freely in a hook race, there is also the problem that the upper thread, or the upper thread loop, can become clamped between the hook and the hook race during the guiding through. In order to make it possible to release the clamped thread, currently the hook has to be removed from the hook race. This is laborious for the operator, and requires a certain degree of dexterity.
In the known hook systems, there is the further problem that the lower thread, which is pulled into the sewed material by the upper thread, briefly accelerates the lower thread bobbin, so that an overrun of the lower thread cannot be avoided. This causes changes in the thread tension that can again result in a non-optimal stitch pattern.